But I think it would need to be more like one in a million or one in a billion. I think even one civilization becoming a slow interstellar (less than 0.1C ships for their) civilization could colonize the galaxy in less than a million years.
Consider what we could do if we could get a slow ship to Alpha Centauri in some absurd time like 1000 years and actually settle there. Maybe we try ever If us here on Earth and Sol could only do that once every thousand years and then if each colony could too. We would only be doubling the amount of stars we inhabit every thousand years. Presuming this slow pace we would also be adding 5~10 light years to our civilization in that time too. But in a million years that 5k to 10 light years would be a sphere with diameter about 10% to 20% the diameter of the galaxy. Allow those jumps to be 50ly and we could get a whole Milky Way galaxy in that time.
That is all predicated on very slow stuff, no FTL, slow ships or project taking massive time. And since the dinosaurs died we had 65 such time periods and another 300 while the dinosaurs lived...
And I could go on for hours about this stuff. But my point is that if unicellular life is common and there is a single great filter and that is the jump to multicellular life then the odds of that event dictate how often we would see other civilizations. A 1 in 1000 we would see civilizations all over the place. We would certainly be withing radio range of at least a few. So it would need to be much worse odds.
That colonisation could of course be in the form of probes simply exploring, but there are timescale and resource issues with that which make me question if it would be worthwhile for a civilisation considering the limited energy in any given system and tremendous effort involved in getting to another once it runs out.
Any proposed great filter to the Fermi paradox needs to be non-exclusive. As in it can't be something that will only impact some of the group, it needs to impact all or very near to all in a statistically significant way.
In the previous example if even just 1% of civilizations wind up having just a subset that go out and explore we would still expect to be able to have seen some here in the Milky Way because that would be 100,000 or so planets or Stars producing multicellular life and with the presumed odds we were discussing civilizations that expand. We presumed for the ease of math, because we're not pulling out the whole Drake equation, that the one in 1000 was just for the one filter. Of course you can do the math with whatever percentages you like at any filter. And each set of numbers you plug in means something slightly different with regards to what we're seeing and why we're seeing it out here in the real world.
https://en.wikipedia.org/wiki/Multicellular_organism#Experim...
I’m a multicellular rare Earther. We’ve had on the order of 10^40 cells, ever [1]. Symbiogenesis occurred, from what we can tell, once [2]. (For comparison, there are 10^11 stars in the Milky Way [3] and 10^24 in the observable universe [4].)
We might be able to argue that factor should be cut, since any late symbiogeneses would be outcompeted into oblivion. But that still, optimistically, puts us in the realm of the Milky Way’s star count.
[1] https://www.cell.com/current-biology/abstract/S0960-9822(23)...
[2] https://en.m.wikipedia.org/wiki/Symbiogenesis
[3] https://en.m.wikipedia.org/wiki/Milky_Way
[4] https://en.m.wikipedia.org/wiki/Observable_universe#Matter_a...
Intergalactic travel is borderline impossible barring unknown physics or travel very close to the speed of light. Even at speeds like 0.5c (50% the speed of light) the trip would take so long you'd have problems like cosmic rays tearing you apart over such long spans of time, and in the vastness of intergalactic space there's no place to pitch a tent and chill and repair things. 0.5c would get you to the stars but not the galaxies.
Intergalactic flight would require something more like 0.95c to 0.99c. The energy requirements for that are insane and possibly unachievable, and if you hit a dust particle at that speed the yield will be like a thermonuclear bomb. The cosmic microwave background also becomes a beam of hard gamma rays aimed at your head. All kinds of crazy extreme physics things happen.
Lastly, why do it? Galaxies are huge and if you're alone then it's all yours. The only conceivable reason would be to flee some galactic-scale super-catastrophe like your galaxy's central black hole behaving badly and frying everything with gamma rays. Even for that it might be easier to burrow deeply into planetary bodies instead.
Of course one can imagine ultra-far-future scenarios like: what if Andromeda hosts some galactic-scale super civilization by the time it hits the Milky Way which by then also hosts such a thing. That'd be a hoot.
Why would it require speeds that high? Sure, it's going to take a very long time, but why is that an insurmountable obstacle?
There are enough isolated stars in intergalactic space that one can even imagining making the trip in smaller steps, with colonization in between. At a stellar density nine orders of magnitude lower than our galaxy stars are still within thousands of light years of each other.
And gov’ts and social structures rarely last a few generations, let along 100 of them.
Not to mention inbreeding.
What makes you think any humans stuck in something the size of even the most generously sized starships won’t go full lord-of-the-flies and be unable to effectively maintain the ship long before it ever arrives?
Do I suspect we'll see life commuting between galaxies, seems unlikely life as is fragile compared to how damned harsh space is.
But intelligence is a completely different story. We send rudimentary intelligences to space and have racked up billions of miles on them. It seems far more likely that any space faring civilization would look like the following.
1. They would ship the instruction to build life when the reach the destination they are heading too. Machines with error correction seem much more resilient would be much more likely to reach a destination if they had enough energy for the trip so they could refurbish themselves over time.
2. Getting rid of the bodies/life part in the first place. Who cares if it's a million years if you can just pause yourself?
Of course the fact the entire universe isn't filled with Von Neumann probes (at least that we see) points out that this hasn't happened yet.
And having a general purpose system capable not only adapting to all the various situations and challenges likely to be faced, that also would have the reserves to deal with them usefully AND reproduce is something we can only hope for in our dreams right now.
And until such a thing exists, it’s only speculation it wouldn’t have similar types of problems, eh?
Humans are the most adaptable and intelligent anything we have yet run across, and we still regularly struggle to solve the problems we run across even in our comfy and well known existing biosphere which is right here, and that we’re quite well adapted to.
And that is assuming a one way trip. Energetically, what could it hope to return to us that would be worth the cost we’d sink into it to try?
Panspermia/species wide genetic reproductive drive, maybe - but then sending a robot doesn’t scratch that itch does it?
2) opportunity cost of time is a thing. Some would argue even that time itself is the most valuable thing we have. Pausing yourself for a million years while your competitors don’t, could be a real problem. Also, think of all the new TV shows you’d miss!
Agree on the von neumann probe problem. The lack of them doesn’t lend credence to it actually being straightforward or even possible solution for sure.
But hey, maybe all the UFO folks are onto something, warp drives/wormholes exist and are cheap, etc.
In which case, disclose it already assholes so we can start doing cool stuff with it!
A colonized galaxy will have people mostly living in artificial habitats. A starship of sufficient size is just an artificial habitat moving at high speed.
One would get around the issues you discuss by just sending multiple vehicles. And anyway, this is in rebuttal to the idea that intergalactic colonization is impossible. The onus on that argument is to show it can't work, not argue there are obstacles that would make it uncertain in any particular case.
Your claims that all this is easy and entirely possible - has no evidence, because near as we can tell we haven’t seen anyone visiting us or anywhere we’ve seen with any of these setups. And we haven’t successfully gone even beyond our moon with a manned mission.
I don’t think anyone is claiming intergalactic colonization is impossible.
All I’m saying is it doesn’t seem worth the cost, by any metric we currently have, or straightforward to actually do, based on our current understanding of physics.
And that there are a lot of real issues with trying to do it that would make it unlikely to succeed if we tried right now, without making it even more costly.
Where did I say that? I didn't.
> I don't think anyone is claiming intergalactic colonization is impossible
Let's look at what they actually said:
> Intergalactic travel is borderline impossible barring unknown physics or travel very close to the speed of light.
And I was arguing against that claim, which I believe is clearly spurious. You seem to agree with me on that.
> All I’m saying is it doesn’t seem worth the cost,
I don't see it as fundamentally different from interstellar colonization in that respect. Anyway, lots of things are done for the hell of it, and on the scale of a galactic economy an intergalactic colonization program would be less than pocket change.
There is nothing we are aware of that is even close to expensive/worthwhile enough (except perhaps information) to justify the cost in energy to move it that distance. Even if the energy is essentially free.
Do the math - rocket fuel isn’t very expensive in bulk, but even moving ‘free’ gold, platinum, iridium, etc. is not even close to worth it.
And information can be gathered with telescopes or transmitted with lasers or radio at faster speeds, so why bother with the trek?
What math are you on? The entire reason moving the "free" ore in the asteroid belt to Earth is expensive is propellant. If we had cheap interplanetary transport, it would absolutely make sense to mine and return matter.
Which we don’t. And how do you expect to get it? Especially when the ‘cheap’ part is already too expensive to make it cost effective even within our own neighborhood?
That’s the point!
You might as well complain there is no point in being poor when you could just be rich. Or that I could take all vacations I wanted if it was free to take vacations. Thanks?
I mean just looking at the energy expenditure growth rate of Earth, you spend as much energy as kings used to in a day. And there is still an absolutely massive amount of solar energy left to harvest.
Might want to keep workshopping that one.
The best way to extract detailed information about a star system is to colonize it. Remote sensing only goes so far.
Then think for a moment about all the other things we’d probably prefer to do with such a monstrous amount of energy. That’s the opportunity cost, even if that energy is free.
We’re entirely speculating on that colonization part - we’ve never tried it.
A fantasy that even if it happened, would be competing with other things - like powering future air conditioning, or the equivalent of 3D porn, or solving world hunger, or building more aircraft carriers, or the like.
So will never be free or actually infinite eh? That’s the opportunity cost part of the equation.
I propose we should, since any subgroup that doesn't grow will be overshadowed by groups that do. If propensity to reproduce has a genetic component it will be selected for.
I think the underlying question is ‘when would such a course of action (interstellar travel) be more preferable than the alternative’.
We could have growth to near infinity and still have interstellar travel be inferior to all our other options, based on our current understanding of physics.
I’m pointing out that relative benefit and cost matter and tend to drive decisions - and that the massive cost with (currently) no plausible benefit which could outweigh it, makes it unlikely we would end up taking that course.
Unless we discover new physics, or new ‘value’ somewhere which would justify it.*
Energetically, for instance, even if we found a planet of pure most expensive thing we can think of (except perhaps for antimatter, though that is a more complicated discussion) just a few light years away, it would never be economic to go get it based on our current understanding of physics.
Even sending a physical probe would be of dubious value, especially considering everyone who would be alive or benefit from anything it could ever provide (including information) would be long dead before we could even find out if it could talk to us over those distances or had arrived.
This is so obvious, btw, that sci-fi writers always have to come up with new physics (or outlandish extrapolations of current thoughts on potential physics - see the Expanse’s Epstein drive, or Star Trek warp tech and subspace communications) for the story to be even a little plausible or interesting. [http://toughsf.blogspot.com/2019/10/the-expanses-epstein-dri...]
And it always has to be a mcguffin, because otherwise the whole story falls apart.
For example, in The Expanse, the Rocinante’s drive would have to output 60+ TW of power for even a moderate burn (2G). Something even the most basic mining rockhopper is supposedly capable of, and folks are regularly shown in poverty type living conditions while being those rock hoppers.
The amount of power produced from just that one engine in that universe in an hour or less would be sufficient to distill enough water, power enough hydroponic grow farms, and synthesize enough chemicals, to feed and hydrate literally hundreds of millions of people. Maybe a billion, if sufficiently efficient.
The United States currently consumes a total of 4 trillion Terawatt hours a year [https://www.eia.gov/energyexplained/electricity/use-of-elect....], and at that engines moderate 60 TW power output level, it would produce energy equivalent to our current entire yearly electrical energy usage every 4 minutes. And they’re shown, in context, doing half that rate as a matter of course for weeks. Even if we converted that to electrical energy in the most absurdly inefficient way possible (boiling water to drive steam turbines), it would produce that degree of electrical power every 15 minutes.
Does the Expanse make any sense at all, if each individual ship is burning more than the energy equivalent of all the clean water, food, drugs, and electrical power the entire Earth needs for a year every single week they operate normally? Or for some of those ships, every minute? Especially when there are shown to be thousands or even hundreds of thousands of such ships operating at once, by a vast array of different powers and interests?
And that Earth, despite having access to all that tech, and building 1000s of those engines (at least), grows crops in open fields and suffers massive famines due to… winter conditions? Due to an asteroid impact? And sometimes just because? And has severe water rationing even for the political elite?
Earth is show to have a pretty dysfunctional (and neglectful) political system, but even they couldn’t pull that degree of insanity off.
And belters worry about using mirrors on Ganymede, when just going to and from Ganymede requires using 4+ orders of magnitude more energy than they would if they used enough grow lights to be getting complaints from Earth about the light pollution.
And a 10,000 year voyage at slow rates to go somewhere that has nothing that justifies the insane cost to do it, with no ability to communicate on timescales equivalent to even the whole of human recorded history, is not a very interesting story. Such a voyage, based on our current track record with technical reliability or social stability is even less likely to succeed.
It’s the economic equivalent of heating your house by burning shovel fulls of $100 bills in your fireplace - because you can’t pay your $150/month heating bill.
Even Mr. Musk eventually decided he’d rather buy Twitter than actually try to colonize Mars, yeah? And relatively speaking, Mars is right there and way friendlier and more interesting in every way than interstellar space.
Actual interstellar space travel seems more and more like the equivalent of the 50’s idealism around powering your hairdryer with a micro-nuclear reactor.
* Notably, sometimes ideology and propaganda can push society into doing really weird things. But even the Crusades had a real macroeconomic and sociological basis for why they needed to happen. So maybe at some point, sending politically problematic ‘colonists’ into space to die will be worth the cost. And some might even make it! Eventually. But chances are, we’ll find more cost effective ways to do it.